Drive assemblies for vehicles wherein both propulsion and steering of the vehicle has been achieved by the control of the rotation of drive wheels or gears have been employed in conjunction with tracked vehicles such as tanks. Such drive assemblies may also be employed in conjunction with wheeled earth moving or farm vehicles as disclosed in U.S. Pat. No. 4,184,387.
In transmission systems for these vehicles an engine drive shaft engaged a propulsion or speed change gear unit as well as a steering unit. The propulsion unit drove secondary transmission components including a main shaft which was oriented transversely to the engine drive shaft; the main shaft engaged a pair of planetary differential gears. The steering unit superimposed steering control on the planetary differential gears through a zero shaft. The zero shaft also lay perpendicular to the engine output shaft. Each planetary differential gear drove a vehicle track, chain or drive wheel.
Typical examples of prior tracked vehicle transmission systems were illustrated in U.S. Pat. Nos. 3,966,005, 3,601,211, 3,534,635, 3,425,296 and 3,373,636. Additional examples of similar transmissions for tracked vehicles are shown in United Kingdom Pat. Nos. 1,296,666, 1,155,867, 1,126,782 and 978,037.
In prior drive assemblies with gear output shafts lying on axes transverse to the engine drive shaft, the transmission casing was interconnected to the engine casing by mating flanges at the shaft end of the engine. Since there normally was also an engine flywheel assembly between the engine and transmission, the entire drive assembly was of substantial length, occupied significant vehicle space and thus detracted from the total useful interior space of the vehicle and mandated large, heavy and inherently costly vehicles.